Add-on locking assemblies for automotive or building use are well known in the art and usually comprise a two-part hasp, with one part mounted on a surface of a stationary portions of a door structure and the other part mounted on a surface of a movable portion of the door structure, one of the parts of the hasp being formed as an eye which traverses a slot formed in the other part, a padlock being used to engage the eye and lock the assembly, the anchoring of the hasp parts to the surfaces being done with bolts or screws or the like.
In another version of the known assemblies, a pair of identical hasps are used, one mounted on the surface of either portion of the door assembly, each hasp being L-shaped and each having a flange projecting outwardly from the door structure adjacent one another and each formed with a respective aperture in alignment with one another and traversed by the shaft of a lock of the type having a cylindrical body formed with an elongated groove across which the shaft can move transversely, the two flanges fitting into the groove. As an alternative to the cylindrical type lock, a padlock can be used with the shackle thereof passing through the apertures.
A number of security disadvantages are encountered with these types of locking assemblies, namely, the surface mounted hasps are prone to being pried off the mounting surfaces either entirely or to the extent that a saw blade or bolt cutter can be inserted between the surface and the hasp, and the mounting bolts severed. Alternatively, a hammer and chisel can be used to remove the heads from the bolts, or the bolt cutter or saw blade can be used to sever the shackle of the padlock.
While the cylindrical-bodied lock offers the best protection against a direct attack on the lock shackle or shaft itself, the body of the lock presents a special disadvantage when used with surface mounted hasps in that the rather large cylindrical body provides an ideal structure behind which a pry bar can be inserted and brought to bear, separating the hasps from the mounting surfaces.